This invention relates to circuit protection devices and methods, and in particular embodiments, to circuit protection devices and methods for use during radiation sterilization of devices containing electronic circuits.
Over the years, sterilization of medical devices has become more important and difficult. At one time it was possible to sterilize most medical devices at the site of use, since the devices were relatively simple, such as reusable syringes, scalpels, scissors or the like. In addition, the medical devices were often used in a doctor""s office, hospital, or the like, that included sophisticated sterilization equipment. Thus, the medical devices could be shipped for use without sterilization.
However, medical devices have changed considerably over the years. For instance, the devices are becoming more complicated and use many different materials, such that autoclaving, chemical sterilization, or the like, is no longer possible, since the processes would likely destroy the materials of the medical device or fail to reach areas not readily accessible after construction of the medical device. In addition, many medical devices are now being used in the home by patients, and these patients generally do not have the equipment necessary to perform the required sterilization. Thus, on-site sterilization has become difficult or impossible to perform at the site of use.
To overcome this drawback, most devices are now sterilized at the facility of manufacture, prior to shipment. Sterilization can be facilitated by sterilization of each component prior to assembly in a sterilized environment. However, additional sterilization is often required. Heat and chemical sterilization cannot always be used due to possible destruction of the various materials. To overcome issues of heat and chemical sterilization, radiation (including x-ray and electron beam) sterilization was developed to provide sterilization of a medical device once it was in its packaging. Thus, after sterilization, the device is shipped and stored in a sterilized environment until the medical device is to be used.
Although radiation sterilization has solved many sterilization issues, it is difficult to sterilize complicated devices containing electronic circuits, since the radiation has the capability to damage or destroy semiconductor circuit elements. One approach is to remove the circuits prior to sterilization, but this still raises issues of sterilization when the device is reassembled.
It is an object of an embodiment of the present invention to provide an improved circuit protection device which obviates for practical purposes, the above mentioned limitations.
According to an embodiment of the invention, a circuit protection device for protection of sensitive components during high energy sterilization that includes a support substrate and a protective housing. The substrate supports the sensitive components. The protective housing is hermetically coupled to the support substrate to seal the sensitive components within the protective housing. Preferably, the protective housing stops high energy used in the high energy sterilization from damaging the sensitive components from a predetermined exposure level of high energy sterilization. In further embodiments, the circuit protection device includes a protective conductor that is coupled to the support substrate on a side which is opposite the protective housing to prevent high energy from entering the opposite side of the support substrate. The circuit protection device can also include an energy absorbing material contained within an area sealed by the protective housing to absorb high energy byproducts produced by the protective housing stopping the high energy used in the high energy sterilization. Preferably, the support substrate is a circuit board, and the sensitive elements are semiconductors. Also, the high energy sterilization is E-beam sterilization and the high energy are electrons, and the high energy byproducts are x-rays.
In particular embodiments, the energy absorbing material is an epoxy containing metal. Also, the protective housing and protective conductor are formed from a metal or other electrical conductor. For instance, the metal is selected from the group consisting essentially of titanium and aluminum.
In particular embodiments, the predetermined exposure level is above 2.0 Mrad. Alternatively, the predetermined exposure level is less than or equal to 5.0 Mrad, or the predetermined exposure level is above 0.5 Mrad.
In another embodiment of the present invention a circuit element for use in an electronic device includes a semiconductor structure. The semiconductor structure has been sterilized by a predetermined dosage of radiation. Also, the gain characteristics after radiation sterilization are reduced by less than a predetermined fraction of before radiation sterilization gain characteristics. In addition, after radiation sterilization the characteristics of collector current and base current as a function of base voltage change in a generally proportional relationship relative to each other. In preferred embodiments, the radiation sterilization is by gamma radiation. In particular embodiments, the circuit element is a transistor, a circuit array, or a PNP high voltage structure.
In further embodiments, the predetermined fraction of before radiation sterilization gain characteristics is 25%, 50%, 75%, or the like. The predetermined dosage of radiation is above 5 kGy, 10 kGy, 15 kGy, 20 kGy, 25 kGy, 30 kGy, or the like. In other embodiments, a ratio of the collector current and the base current, each as a function of the base voltage, has a magnitude greater than one for a predetermined operating range.